Superheterodyne receiver



June 17, 1930.

YW, VAN B. .ROBERTS SUPERHETERODYNE RECEIVER Patented time A17,1930

Unirse STATES Nrererrif1or-rice N Y WALTER vAN B. ROBERTS, OE PRINCETON, NEW JERSEY, nssrofNoRY To RADIO coR- PORATION or AMERroaA CORPORATION OE DELAWARE SUPERRETERODYNE REcEIvER `Application Vfiled March 29, 1929. SeriaI No. 350,947.4

The present vinvention lrelates to heterodynejreceivers, and, more particularly, to a superheterodyne receiving circuit Vwherein signals arereceived only at one of the two possible oscillation frequencies employed to produce beat notes.,` i MR It is Often `desirable,in heterodyne receiving circuits, especially in the case of a superheterodyne receiver, to limit lthe heterodyning oscillations to one of the two possible frequencies which it is'found necessary to employ in conjunction with-al predetermined signalfrequency, to secure aparticular beat,

difference of intermediate frequency;` It is to beappreciated that the need for devising a system for accomplishing such a limitation, is pressing because of the fact that in normal operation of a local oscillator more Vthan one possible heterodyning frequencyis secured. The disadvantage in permitting the existence of vtwo possible heterodyning i. 'frequencies'resides in the fact that the same station maybe received on two points of the dial, thus confusing the operator.

Accordingly, it is one of the mainobjects of my present invention to provioe a method of, and novelrneans for,fbalancing the effects of heterodyne voltages on grid and plate of a frequency changer, for one of the possible of producingthe said two possible hetero-` dyning frequencies, in su ch 'relationship that when the'grid. circuit is tuned to the desired signal frequency, lthe impedance beftween the grid` andfilarnent, at the lower possible heterodyne frequency, is anrinductive reactance, whereby fthe eifectivenessof the lower heterodyning frequency inthe production of -beats is substantially eliminated,

heterodyne frequencies, while they are notV and onlythehigher possible heterodyne frequency permitted to be active.

The novel features which I believe to'be characteristic of my invention are setA forth in particularity in the appended claims, the

invention itself, however, as to both its organization and method of :operation will best be understood byv reference tothe following ldescription taken in connection with the drawing in which I have indicated diagrammatically two circuit Vorganizations whereby my invention may be carried into effect.

In the drawing,

Figure l shows diagrammatically a heterodyne circuit embodying one form of my invention,

Figure 2 is a diagrammatic circuit embodying amodified form of the invention. Referring now to Figure1-,`it will" be observed that a localoscillator l is shown cou- Vpled to the plate circuit of a frequency changer 2, which frequency changer is an electronic discharge tube of the well known screen-grid type. A variableV capacity C is connected between the grid and plate of the tube 2 it being observed that the screen element of the tube isproperlybiased by a battery fS,lin the well known and con-` ventional manner. AThe input circuit ofthe Vfrequency changer 2 is Vtuned by a variable capacity C1, the tuned circuit being coupled,

Vas shown at Mto'aA grounded antenna circuit A, G.

The plate of the tube 2 is energized by a source B, theoutput Vcircuit of the tube 2 being coupled to Van intermediate frequency amplifier by a coupling M1. A capacity C2 is shuntedacross the primary coil of the coupling M1 to bypass the radio frequency currents ofthe incoming signal. The out put fromthe amplifier is detected and employed in any type of utilization means, such as phones or a loud speaker, in the well. lrnownrrnanner. Y

The operation ofthe "circuiti -is q best eX- plained by considering the circuit from the Y View-point of the variable capacity C.

When, C equals zero, the heterodyne voltage from theoscillator lis impressed on'the plate circuit of the frequency changer tube 2, and it is obvious that either of two possible heterodyne frequencies will give the desired difference or intermediate frequency beat note. Assuming, that signal energy of a frequency equal to 500 kilocycles is being received, and that the desired intermediate frequency is 100 rkilocycles, it is obvious that the local oscillator could generate oscillations of two frequencies (400 and 600 kilocycles) whichwvould combine with the signal frequency to produce a beat note of 100 kilocycles. N ow with the improvements and adjustments made in my disclosed circuit, it

Vis possible to completelyy balance out. the

effectiveness of the lower possible oscillating frequency viz; 400 kilocycles, and only retain the heterodyning effect of 600 kilocycle oscillations.

For, it `will be observed that if capacity C is'increased a oint will be reached where the lower possible heterodyne frequency (400 kilocycles in the example given) imT presses a voltage on the plate, and also a reversed voltage on the grid of tube 2. This phenomenon may be ascribed yto the fact that when the grid circuit is tunednto the signalV frequency, the impedance between grid and filament at theY lower heterodyne frequency,` is an effective inductivereactance. It follows, therefore, that the current flowing from plate vto filament, through the capacity C (which current is QQdegrees ahead in phase of the locally impressed heterodyne voltage) produces a drop across the input circuit, 180 degrees ahead ofthe lower frequency local oscillation voltage.

The capacity C Aisadjusted for'such a value that, not only is the grid potential due to thelocal oscillation opposite in phase to the plate potentialy due to the same oscillations, but isof such magnitude that the two potentials on the plate 'and grid dueto the lower local oscillation neutralize each others effectiveness in producing beats.

.IVhen the local oscillator l is adjusted to nthehigher;of the two possible local frequencies (600 lilocycles in the example given) the grid circuit presents capacitive ref actance to the local oscillations, and the grid potential, engendered by these local oscillations, assists the plate potential in producing'sthe desired. beats. Preferably, the vaheretofore described action would be se cured, it being understood that the basic operation of the circuit would be analogous. It is also to be understood that I am not limited to the use'of a frequency changer of the screen-grid type of tube, inasmuch as I havefound that satisfactory results are obtained in practice with a fixed value of C. For example, this Vfixed capacity may be the grid-plate capacityof an 'or` 'iinary triode tube, such as the' well known UV 201A type of tube.

'In Figure 2, I have shown a circuit embodying the ordinary three element type of tube which operates in a satisfactory fashionvto produce the results described and shown ink Figure l. In *Figurel 2', a frequency changer 3, of the well known three elementrtype has its input Vcircuit tuned by a variable capacityC1, the input circuit bel ing coupled, as at M,to a grounded v'antenna circuit A, G. The filament of, the tube is shown Vheated by a source A, the filament output of the circuitd being controlled by a variable rheostat R1 inserted inthe negative leg of the filament. The output circuit' of the` tube is coupled, Yas jat M1,l to an intermediate vfrequency amplifier, detector, and utilization means.

The local oscillator, in thecircuit shown in Figure 2, embodies electron discharge tube '4 having its` grid connected to the plate circuit of tube 3 by a capacity K, the grid being connected 'to lthe positivevleg of the filament by resistance R, there being a variable resistance R2 inserted in the positive lef of the filament. source of cuirent energi'zes the plateof the tube 4f, the plate circuit of the tube being coupled as at M2 toa circuit inserted in the plate circuit of tube 3. Y

A ley-pass condenser C2 is shunted Yacross the primary of the coupling M1 to by-p'ass radio frequency currents of the incoming signal. It willbe obvious ythat byadjust ing 'the variable capacity C3 any` desired heterodyning oscillations will be produced. In this case, the capacity equivalent to the capacity in Figure 1, is vthe fixed capacity Cf, which is inthis case the internal gridplate capacity of the tube 3, shown in dotted linesV in Figure 2. n 5 y Y i I have found that when the capacity K is ,made equal to .001 1nf'd.,the resistance R is made equal 'to I'O0,000john is,l and the source B has ai potential of"90`vo` lts`, that satisfactory results aire' secured. The -operation of the circuit, as inthecas'e of the circuit in Figure l, involves balancing the effectsof'the lower heterodyney oscillation voltages on the grid land plate of the tube 3, whilethey are not in balance fo'rthe higher heterodyne oscillations. i I l AVVhi'le I# have.; indicated "and described only two' systems for carrying. my invention into effect, it will be apparent to oneslrilled in the art that my invention is by no means limited to the particular organizations shown and described, but that many modifications in the circuit arrangements, as well as in the apparatus employed, may be ma-de without departing from the scope of my invention as set forth in the appended claims. Y

lll/That claim is :v

l. A heterodyne receiver comprising signal energy collecting means, local oscillation means, a frequency changing tube having its grid circuit coupled to the collecting means and its plate circuitl coupled to said local means, a'reactance connected between the grid and plate ofv said tube, said reactance being adjusted tosuch a valuev that the grid potential due to local oscillations of a predetermined frequency is opposite inV phase to the plate potential due to the same oscillations.

2. A heterodyne receiver comprising signal energy collecting means, local oscillation means, a frequency changing tube hav-v ing its grid circuit tuned to signal frequency and its plate circuit coupled to said local means, a capacitive reactance connected between the grid and plate of the tube, said local oscillation means being adjusted to oscillate at the higher of the two possible `frequencies adapted to produce difference frequency beats with the signal frequency, said reactance being of such a value that the effects of the voltages of the local oscillations of the lower frequency on the frequency changer grid and plate are balanced.

3. A heterodyne receiver comprising signal energy collecting means, local oscillation means, a frequency changing tube having its grid circuit tuned to the signal frequency and its plate circuit coupled to said local means, and a variable reactance connected between the grid and plate of said tube. Y

l. A receiving circuit comprisingv signal energyV collecting means, local oscillation means, an electronic discharge means having its grid circuit connected to said collecting means and its plate lcircuitcoupled to said local means, said grid circuit being tuned to the signal frequency, and a variable capacity connected between Vthe plate and grid of said discharge means. A heterodyne receiving circuit comprising signal energy collecting means, a source of local, oscillations,V a frequency changing tube having its grid circuit tuned to the signal frequency and connected to the vcollectinemeans and its plate circuit coupled to the local source, the capacity between the grid and plate of Vsaid tube being employed to balance the effects of heterodyne voltages frequencies produced by said local source.

6. A method of operating a heterodyne f finally, coupling the input and output circuits of s aid chan er in such a' manner that the effectiveness o one of said heterodyning frequencies in the production of said difference frequency is substantially eliminated.

7. A method of operating a heterodyne receiving circuit so that only the `higher of the two possible heterodyne frequencies that might yield a desired difference frequency is permitted to produce an effect in the circuit, which consists in collecting signal energy, producing local oscillations, supplying said local oscillations and signal energy to a frequency changer, resonating the input circuit of said changer to signal frequency, and, finally, capacitively coupling the input and output circuits of said changer in such a manner that the effectiveness of the lower of said heterodyning frequencies in the production of4 said difference frequency is substantially eliminated. Y

8. A method of operating a heterodyne receiving circuit so that only one of the two possible heterodyne frequencies that might Vyield a desired difference frequency is percuit of said changer to signal frequency, and,

finally, impressing voltageson the input and output circuits of said changer in such a manner that the effectiveness of one of said heterodyning frequencies in the production of said difference frequency is substantially eliminated.

9. A heterodyne receiver comprising signal energy collecting means, local oscillation means adapted to produce two possible heterodyne` frequencies that'V might yield a desired difference frequency, an electron discharge tube having its input circuit tuned to the signal frequency and its ouput ycircuit coupled to said local means, and an impedance path between the input and output circuits of said tube for balancing out the effect of one of theheterodyne frequencies inthe production of saidv difference frequency.

Y Y WALTER VAN B. ROBERTS.

on the grid and plateV of said tube for the lower one of any possible pair of heterodyne 

